The present invention relates to electrodes for use in secondary electrochemical cells. More particularly, it concerns a method of making a negative electrode composition and electrode composition made thereby wherein the negative electrode composition includes a lithium-aluminum alloy with a silicon additive.
A substantial amount of work has been done in the development of high-temperature, secondary electrochemical cells. Positive electrodes for the cells have included chalcogens such as sulfur, oxygen, selenium or tellurium as well as their transition metal chalcogenides. Positive electrode materials such as the sulfides of iron, cobalt, nickel and copper are of current interest.
In high-temperature cells, current flow between electrodes often is transmitted by molten electrolytic salt. Particularly useful salts include compositions of the alkali metal halides and/or the alkaline earth metal halides ordinarily incorporating a salt of the negative electrode reactant metal, e.g. lithium. In cells operating at moderate temperatures, aqueous and organic base electrolytes are permissible and these also can include cations of the negative electrode metal.
Alkali metals such as lithium, sodium, potassium or alkaline earth metals including calcium, magnesium, etc. and alloys of these materials are contemplated as negative electrode reactants. Alloys of these materials such as lithium-aluminum, lithium-silicon, lithium-magnesium, calcium-magnesium, calcium-aluminum, calcium-silicon and magnesium-aluminum have been investigated to maintain the negative electrode in solid form and thereby improve retention of the active material at high cell operating temperatures.
One of the areas in the secondary electrochemical cells in which improvement is always required, no matter how small, is in obtaining a higher output voltage of the cell and in obtaining a relatively constant power output during discharge. The present invention was unexpectedly discovered to provide not only improved output voltage, but also to provide a relatively constant power output during discharge.